Pub/Sub with Cloud Functions integration in GCP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Pub/Sub topic named 'my-topic'.

GCP

gcloud pubsub topics create [1]

Drag options to blanks, or click blank then click option'

Amy-topic

Btopic-1

Ccloud-topic

Dpubsub-topic

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different topic name than 'my-topic'.

Omitting the topic name.

The command gcloud pubsub topics create my-topic creates a Pub/Sub topic named 'my-topic'.

2fill in blank

medium

Complete the code to deploy a Cloud Function named 'processMessage' triggered by the Pub/Sub topic 'my-topic'.

GCP

gcloud functions deploy processMessage --trigger-topic=[1] --runtime python312 --entry-point main

Drag options to blanks, or click blank then click option'

Atopic-1

Bmy-topic

Ccloud-topic

Dpubsub-topic

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different topic name in the trigger.

Omitting the trigger-topic flag.

The Cloud Function must be triggered by the Pub/Sub topic 'my-topic', so the trigger-topic flag should be set to 'my-topic'.

3fill in blank

hard

Fix the error in the Cloud Function code to correctly decode the Pub/Sub message data.

GCP

def main(event, context):
    import base64
    message = base64.b64decode(event['data']).decode('utf-8')
    print('Received message:', [1])

Drag options to blanks, or click blank then click option'

Aevent['data']

Bmessage

Ccontext

Devent

Attempts:

3 left

💡 Hint

Common Mistakes

Printing the raw event data instead of the decoded message.

Using the context object instead of the message.

The decoded message is stored in the variable message, so printing message shows the decoded content.

4fill in blank

hard

Fill both blanks to create a subscription named 'my-subscription' for the topic 'my-topic'.

GCP

gcloud pubsub subscriptions create [1] --topic=[2]

Drag options to blanks, or click blank then click option'

Amy-subscription

Bmy-topic

Csubscription-1

Dtopic-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using mismatched subscription or topic names.

Omitting either the subscription name or topic flag.

The subscription name is 'my-subscription' and it must be created for the topic 'my-topic'.

5fill in blank

hard

Fill all three blanks to publish a message 'Hello, Cloud!' to the Pub/Sub topic 'my-topic' using gcloud.

GCP

gcloud pubsub topics publish [1] --message '[2]' --attribute [3]=greeting

Drag options to blanks, or click blank then click option'

Amy-topic

BHello, Cloud!

Ctype

Dmy-subscription

Attempts:

3 left

💡 Hint

Common Mistakes

Using the subscription name instead of the topic name.

Incorrect message text or attribute key.

The message is published to 'my-topic' with the message text 'Hello, Cloud!' and an attribute key 'type' set to 'greeting'.

Practice

1.

What is the main role of Google Cloud Pub/Sub when integrated with Cloud Functions?

easy

A. To send messages that trigger Cloud Functions automatically

B. To store large files for Cloud Functions to process

C. To provide a user interface for Cloud Functions

D. To manage user authentication for Cloud Functions

Solution

1. Step 1: Understand Pub/Sub's purpose

   Pub/Sub is designed to send messages between parts of an app, acting as a messenger.

2. Step 2: Connect Pub/Sub with Cloud Functions

   Cloud Functions run code automatically when they receive messages from Pub/Sub.

3. Final Answer:

   To send messages that trigger Cloud Functions automatically -> Option A

4. Quick Check:

   Pub/Sub triggers Cloud Functions [OK]

Hint: Pub/Sub sends messages; Cloud Functions react to them [OK]

Common Mistakes:

• Thinking Pub/Sub stores files
• Confusing Pub/Sub with UI or authentication
• Assuming Cloud Functions manage user login

2.

Which of the following is the correct way to specify a Pub/Sub trigger in a Cloud Function deployment command?

gcloud functions deploy myFunction --trigger-?

easy

A. --trigger-http my-topic

B. --trigger-bucket my-topic

C. --trigger-topic my-topic

D. --trigger-event my-topic

Solution

1. Step 1: Identify the trigger type for Pub/Sub

   Pub/Sub triggers require specifying the topic name with --trigger-topic.

2. Step 2: Match the correct flag

   --trigger-topic is the correct flag; others relate to storage or HTTP triggers.

3. Final Answer:

   --trigger-topic my-topic -> Option C

4. Quick Check:

   Pub/Sub trigger uses --trigger-topic [OK]

Hint: Pub/Sub triggers use --trigger-topic flag [OK]

Common Mistakes:

• Using --trigger-bucket which is for Cloud Storage
• Using --trigger-http which is for HTTP triggers
• Confusing event triggers with topic triggers

3.

Given this Cloud Function code triggered by Pub/Sub messages, what will be logged when a message with data "Hello" is published?

def hello_pubsub(event, context):
    import base64
    message = base64.b64decode(event['data']).decode('utf-8')
    print(f"Received message: {message}")

medium

A. Received message: event['data']

B. Received message: Hello

C. Received message: b'Hello'

D. Error: 'data' key missing

Solution

1. Step 1: Decode the Pub/Sub message data

   The message data is base64 encoded; decoding it gives the original string "Hello".

2. Step 2: Print the decoded message

   The print statement outputs "Received message: Hello" exactly.

3. Final Answer:

   Received message: Hello -> Option B

4. Quick Check:

   Base64 decode then print = Received message: Hello [OK]

Hint: Decode base64 data to get original message [OK]

Common Mistakes:

• Printing raw base64 bytes instead of decoded string
• Using event['data'] directly without decoding
• Assuming 'data' key is missing

4.

What is the likely cause if a Cloud Function triggered by Pub/Sub never runs after publishing messages?

medium

A. The Cloud Function is not subscribed to the correct Pub/Sub topic

B. The Cloud Function code has a syntax error

C. The Pub/Sub topic does not exist

D. The Cloud Function has too much memory allocated

Solution

1. Step 1: Check the Cloud Function trigger configuration

   If the function is not subscribed to the right topic, it won't receive messages.

2. Step 2: Rule out other causes

   Syntax errors cause deployment failure, not silent no-run; topic existence is needed but usually checked; memory size doesn't stop triggers.

3. Final Answer:

   The Cloud Function is not subscribed to the correct Pub/Sub topic -> Option A

4. Quick Check:

   Wrong topic subscription = no trigger [OK]

Hint: Check topic subscription if function never runs [OK]

Common Mistakes:

• Assuming syntax error causes silent no-run
• Ignoring topic existence or permissions
• Blaming memory size for trigger issues

5.

You want to build a system where multiple Cloud Functions react independently to the same Pub/Sub messages. What is the best way to set this up?

hard

A. Publish messages multiple times to different topics

B. Create multiple Pub/Sub topics, each with one Cloud Function subscription

C. Use one Cloud Function that calls other functions internally

D. Create one Pub/Sub topic and multiple subscriptions, each triggering a different Cloud Function

Solution

1. Step 1: Understand Pub/Sub fan-out pattern

   One topic can have multiple subscriptions; each subscription can trigger a different Cloud Function independently.

2. Step 2: Compare options

   Multiple topics add complexity; one function calling others is indirect; publishing multiple times is inefficient.

3. Final Answer:

   Create one Pub/Sub topic and multiple subscriptions, each triggering a different Cloud Function -> Option D

4. Quick Check:

   One topic, many subscriptions = multiple triggers [OK]

Hint: Use multiple subscriptions on one topic for parallel triggers [OK]

Common Mistakes:

• Creating many topics unnecessarily
• Using one function to call others instead of triggers
• Publishing duplicate messages to multiple topics